The present invention generally relates to a spindle motor. More specifically, the invention relates to a spindle motor utilizing a fluid dynamic pressure bearing to support a shaft within a bearing portion, the shaft being surrounded by lubricating oil enclosed in the bearing portion.
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle the information being accessed by means of read/write heads generally located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside the hub or below the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted by means of two ball bearing systems to a motor shaft disposed in the center of the hub. However, with the decreasing size of information storage systems, other types of bearings including hydrodynamic bearings are being developed.
In these types of systems, lubricating fluidxe2x80x94either gas or liquidxe2x80x94functions as the actual bearing surface between a stationary base or housing and the rotating spindle or rotating hub and the stationary surrounding portion of the motor. For example, liquid lubricants comprising oil, more complex ferro-magnetic fluids, or even air have been utilized for use in hydrodynamic bearing systems. The reason for the popularity of the use of air, is the importance of avoiding the outgassing of contaminants into the sealed area of the head disc housing. However, air does not provide the lubricating qualities of oil. Its low viscosity requires smaller bearing gaps and therefore higher tolerance standards to achieve similar dynamic performance.
Thus, in the case of a hydrodynamic bearing employing a liquid lubricant, the lubricating fluid and its components must be sealed within the bearing to avoid loss of lubricant which results in reduced bearing load capacity. Otherwise, the physical surfaces of the spindle and housing could contact one another, leading to increased wear and eventual failure of the bearing system. Equally seriously, loss of a seal or failure to control the fluid level within the bearing system could cause contamination of the hard disk drive with lubricant particles and droplets as well as outgassing-related condensation.
A further difficulty with prior art designs of liquid lubrication hydrodynamic bearings is that, where fluid reservoirs are not placed in close proximity to the shaft, lubricating fluid can splash onto the shaft and migrate along the shaft into the environment. To prevent this oil migration and/or splashing, various physical barriers have been constructed, extending either from the shaft or the bearing sleeve and precluding fluid from ascending the shaft.
An example of the conventional fluid dynamic bearing structure incorporating a physical barrier for oil migration prevention is shown in FIG. 1(b). As shown in this figure, the shaft 12 is placed for rotation into the bearing sleeve 14. The bearing sleeve has a reservoir 16 formed therein such that an opening of the reservoir is not in close proximity to the shaft 12. An oil barrier 10 is mounted on the shaft to prevent lubricating fluid from migrating along the shaft when the fluid is splashed onto the shaft for example during operational shocks.
Forming this additional barrier structure increases the bearing manufacturing time and cost. Therefore there is a need in the art for a low cost structure preventing lubricating fluid migration.
It is an object of the present invention to provide a fluid dynamic bearing assembly having a fluid trap for oil migration prevention.
In one aspect, the present invention provides a fluid dynamic bearing assembly including a shaft and a bearing sleeve. A bearing gap is formed between the shaft and the bearing sleeve and is filled with a lubricating fluid. A reservoir containing excess of the lubricating fluid is formed at one end of the bearing sleeve. The reservoir is not located in close proximity to the shaft. A fluid trapping recess is formed in the shaft, the fluid trap being configured to prevent migration of the lubricating fluid along the shaft into the environment.
When the bearing assembly experiences shocks during its operation, a small amount of lubricating fluid may be splashed out of the reservoir. Drops of the lubricating fluid will then migrate towards the shaft and will get trapped in the fluid trap. A sharp upper edge of the fluid trap prevents a further upward migration of the fluid into the environment.
The above advantages and features are of representative embodiments only. It should be understood that they are not to be considered limitations on the invention as defined by the claims. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims.